Today we're going to take a collective look at all the conflicting warnings and exhortations we hear about what we should and shouldn't eat. It seems everyone has some pet theory that you shouldn't drink milk, or you have to eat organic, or you shouldn't eat "processed" foods, or you must only eat raw. There are always explanations for why this is: We didn't "evolve" to eat this or that; it isn't "natural" to eat something; our digestive systems weren't meant to handle a certain thing. I know what you're thinking: How is it possible to cover all those possible claims in a single Skeptoid episode? We're going to do it by stepping back from all of the specific claims and specific foods, way back. We're going to look at food as a whole, and study what it's made of, what those bits are, see what we need and what we don't. And then, with this as a foundation, we'll have the tools to effectively examine any given eating philosophy.

Originally, this episode was going to be about the specific claim that we shouldn't drink milk, based on the idea that humans are the only species that drinks another species' milk, and it's therefore unnatural. I've also been given the suggestion — several times — that we should never give pet food to pets, because its ingredients are not the ones they evolved to eat. I quickly realized that all of these notions are basically the same, and all depend on a fundamental misunderstanding of the nature of food. Dog food, beer, cheese, and cake frosting are all compounds that no species evolved to eat. Then how is it that we're able to eat them? In essence, it's because all food — in whatever strange form we want to present it — consists of the same basic building blocks, all of which we did evolve to eat, and all of which are found in nature.

Before we look at these building blocks, I need to state that it's impossible to be 100% comprehensive within the limitations of a Skeptoid episode. There are innumerable subtleties and exceptions and footnotes that I'm not going to go into. Most of these exceptions come from the fact that humans developed in a broad range of environments, and as a result, some groups are more or less adapted to certain compounds, lactose tolerance being an obvious example. People with phenylketonuria can't metabolize the amino acid phenylalanine. Some populations have difficulty synthesizing enough Vitamin D in their skin. These are just examples; there are plenty of others, and I'm not pretending to cover every nuance here. If you want to delve further, see the Further Reading suggestions in the online transcript for this episode. Today's discussion is at a level that applies generally to all humans, and to some degree to most other vertebrates as well.

Food breaks down into six basic compounds. All food consists of combinations of these six, and every one of them is found in nature:

1. Amino Acids

These are the building blocks of proteins. Proteins are essential for our bodies. We need to eat protein, which is then broken down by our digestive system into its constituent amino acids, and then our body reassembles them into whatever proteins it needs. Some amino acids are called essential, and this refers to those that our body cannot synthesize and that we must eat. There are eight essential amino acids, plus about fourteen others that are conditionally essential: needed by infants, growing children, and other certain populations. With few exceptions, the body makes use of all amino acids; there's no such thing as an amino acid that we can't or shouldn't consume. Proteins in food like enzymes and hormones are usually not used by the body as enzymes and hormones; they too are broken down into amino acids which are then gainfully employed as building blocks.

2. Fatty Acids

Like amino acids, fatty acids come in essential and conditionally essential varieties. Omega-3 and omega-6 are the two essential fatty acids that we must get from food because we can't synthesize them, and that have a wide range of important functions throughout our bodies; three others are usually considered conditionally essential for some populations.

All the rest of the fatty acids are ones that we don't need to eat. Our body does usefully employ most of them, but it can synthesize what it needs, so you generally want to minimize your food intake of them. These include saturated fats (where all available chemical bonds are "saturated" with a hydrogen atom) and the non-essential unsaturated fats, which include monounsaturated, polyunsaturated, and trans fats.

3. Carbohydrates

These are your sugars and starches, which all break down into monosaccharides: the single sugars glucose, fructose, galactose, xylose, and ribose. Two of those together may come from a disaccharide like table sugar; a longer polysaccharide chain may come from the carbs in a granola bar. Whatever we eat gets broken down into those monosaccharides (though some populations may have enzymatic deficiencies that hamper the digestion of some combinations, like lactose). Those monosaccharides fuel our metabolism, and are the principal building blocks of the synthesis of other needed compounds. Any extra monosaccharides are put together into space-saving polysaccharides for storage.

4. Vitamins

Exactly what is a vitamin? There's a simple and clear definition. We've just discussed the three basic types of nutrients; a vitamin is any other organic compound that our body needs, that we are unable to synthesize enough of, and that we must get from food. Vitamins were discovered throughout the first half of the 1900's, and each time we learned about a new one, it was given a successive identifying letter: Vitamin A, B, C, and so on. After we learned about Vitamin B we found it was actually eight different vitamins, and so we have Vitamin B1, B2, B3, and the rest. Many animals synthesize these vitamins from proteins and fats, so they don't need to eat such a diversity of different foods to get them, the way we do.

There are two basic kinds of vitamins: water soluble (vitamins B and C) and fat soluble (all the others). If you consume more water soluble vitamins than you need, the excess will be quickly and harmlessly discharged in your urine. Overdosing on fat soluble vitamins provides a bit more of a challenge to your body though, and can lead to hypervitaminosis, which can be dangerous in extreme cases.

With a few notable exceptions, anybody who lives and eats in a modern industrialized country gets more than enough of all the vitamins their body needs, and there's no need to spend money on vitamin supplements. If you eat three meals a day, the buckets in which your body has room to store vitamins are brim full, and vitamin supplementation would be like pouring more onto an already overflowing bucket. Save your money.

5. Minerals

These are defined as the inorganic chemical elements that our body needs. There are sixteen essential elements (chemically, they're not really all minerals) including iron, calcium, zinc, sodium, and potassium. There are some half-dozen others considered conditionally essential, but if you stick with the sixteen you're probably all right. Minerals obviously have to be consumed; our bodies are not atomic reactors and so we can't synthesize chemical elements.

With a very few exceptions, anyone who eats regular meals in an industrialized country gets more than enough of all the minerals they need. Perhaps the two most common exceptions are pregnant women who can benefit from iron supplementation, and people who avoid dairy products and could often benefit from calcium supplementation.

6. Water

Kind of an obvious one. It's the only thing anyone needs to drink — there's no substitute — and most of us get all we need from what's contained in our food and other drinks.

And so, there we have the six fundamental compounds that make up all food. The basic argument against all of the various "You shouldn't eat this or that" claims is that those foods all break down into the same building blocks, building blocks which you would also get from other food. The opposing argument in favor of those claims is that some of these building blocks are good (like essential amino acids) and some are bad (like trans-fat), and we should strive to eat foods that deliver the most good nutrients with the least amount of harmful contents. Kind of a no-brainer, obviously, but it's rarely the argument that's actually made. Instead, the arguments I usually hear call out a particular food based on some ideology rather than its actual contents. Not that there's anything wrong with ideologies, but they should not be misrepresented as food science.

Other than a glass of pure water, there is hardly a food source on the planet that delivers anything less than a radically complex assortment of proteins, lipids, and starches, laced with vitamins and minerals. It's the proportions that differ. Looking at it from this perspective, there's little fundamental difference between milk and orange juice. The orange juice contains more sugar and vitamins but less fat and protein, while the milk contains a more even spectrum of nutrients. An argument like "Cow's milk is bad because early humans didn't evolve to drink it" becomes completely goofy when you consider only this one irrelevant characteristic. The same goes for arguments against manufactured pet food. There is no reason at all why pet food should look like, or come from the same source as, the animal's natural food; so long as it delivers the nutrients the animal needs.

Cooking introduces chemical changes that are, for the most part, the same as the first step in digestion. Some compounds cannot be digested unless they're cooked first to break certain chemical bonds. Most claims that cooking destroys nutrients are wrong; cooking merely starts the ball rolling on what your digestive system was going to do to the food anyway.

One nice thing about being a technological society is that we have the capability to understand food science, and to design nutritious foods that are more attractive and tasty than our ancestors were able to find on the savannah. The bottom line is that if you wish to evaluate any given food's nutritional value, you must look at what it actually delivers. Simply considering where it came from, or who designed it, is not a useful assessment of its actual substance.